E-mail this article

Sending your article

Your article has been sent.

WESTON — Pipes joined by clamps similar in design to the one that fractured catastrophically last weekend, disrupting Greater Boston’s drinking water supply, had previously leaked in five other locations in the region’s water system, according to a settlement agreement obtained by the Globe.

As a result of those leaks in Newton early in the past decade, the Massachusetts Water Resources Authorityreplaced the clamps with other connectors and then negotiated with the companies that manufactured and installed them to reinforce 23 other water main joints that had the same type of Depend-O-Lokclamp, according to the MWRA and the 2005 settlement document. The water authority did not, however, require any extra fortification for a much larger Depend-O-Lok clamp holding together two massive water pipes several miles away in Weston, where last week’s rupture occurred.

That break occurred in the roughly 150-foot-long section of pipe that serves as the main passage between the seven-year-old MetroWest tunnel and the much older City Tunnel that carries water from the Quabbin and Wachusett reservoirs on the last leg of its journey into Boston. Water authority officials say it is one of the three most critical junctions in the Eastern Massachusetts water system and internal water pressures there are near the highest in the pipe network.

Documents obtained by the Globe and interviews with those involved in the Weston pipeline’s construction also show that the failed clamp was not the project designers’ first choice. The pipes were originally supposed to be much more rigidly connected and encased in concrete but that method couldn’t be used because, as often happens at job sites, the massive pipes to be joined didn’t align perfectly. That led to the use of the more flexible Depend-O-Lok clamp.

MWRA executive director Fred Laskey said in an interview late Friday that there had been no reason to reinforce the Weston pipe joint after the earlier Newton leaks. That’s because those leaks occurred where clamps connected old, pitted pipes to new ones, a particularly challenging environment, he said. The new failure occurred where a clamp held together two new pipes. Engineers, he said, were convinced the clamp on the new pipes would suffice to make the connection watertight.

“Two engineering firms signed off on it,’’ Laskey said. Plus another MWRA official said there had been no other problems with Depend-O-Lok in the system other than Newton.

But on May 1 at 10:01 a.m., MWRA workers received an alarm about a power loss at the Weston site. Four minutes later, workers in the agency’s Chelsea command center, watching a surveillance camera, saw water bubbling out of the ground. Gauges showed water flows had abruptly doubled: It was a major break.

In the end, millions of gallons spurted from a roughly 1-inch gap between the underground pipes where the clamp broke free, prompting one of the nation’s most widespread boil-water orders in recent years. Boston and 29 other communities went without reliably safe tap water for two and a half days.

It remains unknown what caused the large Depend-O-Lok clamp to give way or whether the break could have been prevented. MWRA officials are searching through microfilm and boxes of documents, as well as interviewing staff for information on the clamp and the overall design of that section of the water system.

Contractors are dredging the Charles River to find the steel clamp and its eight bolts, which may be buried under tons of soil dumped by the gushing water. A yet-to-be-appointed independent commission will need the pieces to figure out why it gave way.

The search for answers might also take investigators to Washington and Elm streets in Newton.

A problem in Newton

The project wasn’t easy — connecting pipes almost three-quarters of a century old to new ones to ensure drinking water would be reliably delivered to Newton and nearby communities for 50 more years. Depend-O-Lok clamps were used in 28 locations to hold old and new pipes together and provide a watertight seal.

Installed around 1999, the first clamp, or coupling, failed in 2000, and two others didin 2001, according to a letter MWRA sent Pennsylvania-based Victaulic, one of the world’s leading manufacturers of water system supplies. In 2003, two more “failures’’ occurred, this time costing the MWRA almost $100,000 to replace, the letter said. Some of the failures caused “tremendous disruption’’ to businesses and residences in the area, according to the MWRA.

In its 2004 letter,MWRA placed the blame on Victaulic, saying its clamps failed to deliver a watertight seal, and W. Walsh Co., which installed the clamps, for recommending the brand in the first place. The water authority replaced the five clamps with other types of connectors and demanded the companies pay for that work and for “any future failures.’’Both companies vigorously denied fault, saying there were other reasons for the leaks and there was no need to replace all the clamps.

“The evidence does not support the MWRA’s conclusion that the [clamps] failed,’’ wrote Brian P. Bissey, Victaulic vice president and general counsel.

A Walsh lawyer wrote that the MWRA and its designer signed off on the couplings — and implied the MWRA itself was in part to blame for some of the failures because of a delay in placing a concrete seal over the pipe system and its failure to shut down a main when it was repairing another leak.

In the end, Victaulic and Walsh agreed to reinforce the pipe connections with an interior seal. The repairs worked, and no other problems have been reported. No money was exchanged between the companies and the MWRA, and the settlement documents did not place blame on any of the parties.

Late Friday, Eric Luftig, Victaulic director of marketing and communications, provided a statement acknowledging leaks earlier this decade at the Newton locations where the company’s clamps were used. But he said there had been no finding that the clamps were to blame and that the company complied with the MWRA’s request for help as a matter of customer service.

The clamps in Newton were 5 feet in diameter compared with the 10-foot-diameter clamp used in Weston — and some components of the Weston clamp were made with heavier, bulkier pieces of steel, according to Victaulic’s brochures. “Different size, different design, for different situations,’’ Luftig said.

A representative of Attleboro-based W. Walsh Co. could not be reached for comment.

Now, in the aftermath of last weekend’s massive rupture, MWRA officials are examining Depend-O-Lok clamps throughout the system.

Laskey, the MWRA executive director, emphasized that there has been no determination of the cause of the May 1 break. “We’re still intensely focused on investigating the cause,’’ he said.

Numerous theories about the rupture’s cause have been floated, including excessive ground movement that jostled the pipes or some sort of major corrosion.

A complicated place

The rupture’s location was a trouble spot from the start.

Millions of gallons of rushing water must make a slight turn there. Nearby train tracks can deliver stray electrical currents through the ground, which over time could corrode the pipe system. And the pipe rests in soil that could shift over time from earthquakes or flooding.

MWRA officials said the original design called for the two steelpipes to be rigidly bolted together and encased in a block of concrete. But the pipe segments wouldn’t align properly, according to MWRA officials. That meant if the pipes moved at all within the concrete, the enormous pressure of rushing water could push unevenly against the seal, eventually weakening it.

So project managers changed the design during construction, choosing a clamp system that would allow the pipes some freedom of movement. The first Depend-O-Lok clamp installed failed water pressure tests. Project managers then used a slightly different version. It held until last weekend.

MWRA officials defended their decision to use a clamp.

“It was absolutely an appropriate design change,’’ said Michael J. Hornbrook, chief operating officer for the water authority. “The coupling that was used was what should have been used, given all the conditions.’’

The pipes have now been welded together — and encased in concrete much like in the original design. Water authority officials say it will hold.